This invention relates to method and apparatus for producing synthetic gas that can be used for various purposes, such as heating, reducing, chemical synthesis or reaction, and more particularly method and apparatus for producing such gas by using a large volume shaft furnace which is preferably a blast furnace.
The invention may be used for the production of large quantities of gas that may be used for various purposes, as for fuel gas for heating purposes, or as a reducing gas useful in the metals industries, or gas high in hydrogen and carbon monoxide suitable for the production of methane, methanol, gasoline, or as a starter material for chemical synthesis, or a shifted gas high in hydrogen content for ammonia synthesis as for fertilizers, or for hydrogenation of coal or oil to produce other useful gases or liquids or peterochemicals. However, it provides important high temperature advantages when used for heating purposes as in steel mills, and therefore, it will be discussed hereinafter primarily in connection with such use.
Shortages of natural gas and fuel oil, both current and future, have caused and can cause far-reaching and troublesome problems in the steel making industry which has heretofore used natural gas or fuel oil in substantial quantities for heating purposes, such as soaking pits and reheating furnaces, or for performing or aiding in performing reduction of iron oxides, and for other purposes.
Natural gas has been desirable not only because of its convenience in handling, but also because of its cleanliness and because its products of combustion in general do not provide problems from the environmental standpoint. Availability of suitable gas for use in steel making therefore is of major concern in the steel making industry.
The present invention provides method and apparatus whereby suitable synthetic gas for steel making activities can be produced in large quantities by using a blast furnace as a gasifier, preferably with minor modifications that can be such as to permit the furnace to be used either as a gasifier, or alternatively in the usual manner for reduction of iron oxides to produce metallic iron with the advantage of coal and oxygen injection.
The present invention provides important advantages. The rate of production of gas produced by a blast furnace used as a gasifier according to the invention can be far greater than the rate of production of gas by the largest available commercial gasifiers heretofore used. Since the invention makes possible the use of existing blast furnaces, particularly those which are not used because of economic conditions or obsolescence, it provides gasifiers having low capital costs. Moreover, the invention makes possible the production of gas with minimal carbon dioxide, and thus provides a potential for maximum utilization of carbon and oxygen. It also makes possible substantially complete removal of sulfur from the gas. The invention also makes possible the production of usable gas from various solid and liquid fuels such as coal, coke, fuel oil, or of by-product or waste materials such as low grade or undersized coke, selected municipal wastes, basic oxygen furnace slag, open hearth slag, and other materials of low economic value.
When modified and operated according to the present invention, a smaller, usually obsolete, blast furnace can generate four to six times as much gas as the largest presently operating commercial gasifier, while a blast furnace of the largest size presently operating can generate more than thirty times as much gas as the largest commercial gasifier now in operation, at much lower costs of capital investment and operation.
Gas that is normally produced by blast furnaces when operating to reduce iron oxide has a calorific content of about 85 BTU/SCF, too low for general industrial purposes. The process and apparatus of the invention, on the other hand, can produce gas having a BTU content of about 300 to 450 BTU/SCF or even higher, which makes this gas useful in most industrial services.
Moreover, blast furnaces used to produce gas according to the invention for use in steel mills are generally located in close proximity to other industrial locations, where availability of surplus gas is highly advantageous.
The time required to place blast furnaces in commercial production as gasifiers can be a minimum because of the availability and strategic location of existing idle furnaces.
Use of blast furnaces as gasifiers makes possible utilization of commercial technology in the conversion of coal and by-product industrial fuels to synthetic fuel gas in the large quantities that industry requires, at minimum cost, in minimum time, and with maximum efficiency.
The present invention therefore provides a practical, economical alternative to production curtailments and unemployment caused by shortages of natural gas or other fuels. Gas produced according to the present invention can meet both industry needs and satisfy enviromental requirements.